Vitamin B12 Deficiency
Medically reviewed on February 1, 2018
What Is It?
Vitamin B12 is needed to produce an adequate amount of healthy red blood cells in the bone marrow. Vitamin B12 is available only in animal foods (meat and dairy products) or yeast extracts (such as brewer's yeast). Vitamin B12 deficiency is defined by low levels of stored B12 in the body that can result in anemia, a lower-than-normal number of red blood cells.
Vitamin B12 deficiency can develop for the following reasons:
Absence of intrinsic factor, also called pernicious anemia — Intrinsic factor is a protein secreted by cells of the stomach lining. Intrinsic factor attaches to vitamin B12 and takes it to the intestines to be absorbed. An absence of intrinsic factor is the most common cause of pernicious anemia. Absent intrinsic factor is often associated with a condition called atrophic gastritis, a thinning of the lining of the stomach. Atrophic gastritis is more common in elderly people of African-American or Northern-European descent. In these people, pernicious anemia develops at about age 60.
In children, decreased levels of intrinsic factor can be an inherited (genetic) condition. When this happens, low levels of intrinsic factor produce symptoms of juvenile pernicious anemia in patients younger than age 10.
Pernicious anemia occurs more commonly in people who already have diseases that are linked to immune-system abnormalities, such as Graves' disease, hypothyroidism (under-functioning thyroid gland), thyroiditis (inflammation of the thyroid), vitiligo and Addison's disease (adrenocortical insufficiency).
Removal or destruction of the stomach — Vitamin B12 deficiency can develop in people who have had surgery to remove part or all of the stomach.
Overgrowth of bacteria — Some people develop vitamin B12 deficiency as a result of conditions that slow the movement of food through the intestines (diabetes, scleroderma, strictures, diverticula), allowing intestinal bacteria to multiply and overgrow in the upper part of the small intestine. These bacteria steal B12 for their own use, rather than allowing it to be absorbed by the body.
Dietary deficiency — Vegans (strict vegetarians who do not eat any meat, fish, egg or dairy products) can develop vitamin B12 deficiency because they lack vitamin B12 in their diets. In patients with bulimia or anorexia nervosa, vitamin B12 deficiency also can be related to diet. However, your liver can store vitamin B12 for up to five years, so it's rare for diet to cause this anemia.
Symptoms tend to develop slowly and may not be recognized immediately. As the condition worsens, common symptoms include:
Weakness and fatigue
Light-headedness and dizziness
Palpitations and rapid heartbeat
Shortness of breath
A sore tongue that has a red, beefy appearance
Nausea or poor appetite
Yellowish tinge to the skin and eyes
If low levels of B12 remain for a long time, the condition also can lead to irreversible damage to nerve cells, which can cause the following symptoms:
Numbness and tingling in the hands and feet
Your doctor will ask you about your diet and about any family history of anemia. Your doctor also will review your medical history for medical illnesses (diabetes, immune disorders) or surgeries, such as stomach removal, that can lead to B12 deficiency.
Your doctor may suspect that you have vitamin B12 deficiency based on your medical history and symptoms. To confirm the diagnosis, he or she will examine you and order laboratory tests. During the physical examination, your doctor will look for a red, beefy tongue, pale or yellowish skin, a rapid pulse and heart murmurs resulting from an anemia-related increase in blood flow demands on the heart. Laboratory tests will include:
Standard blood tests to measure the level of red blood cells and check their appearance — In vitamin B12 deficiency, red blood cells are unusually large and appear abnormal.
Blood tests to measure B12 levels — Levels of iron and folate also may be measured to check for deficiencies in these nutrients.
Blood test to measure methylmalonic acid level — The blood level of methylmalonic acid increases when a person has B12 deficiency.
Blood tests for intrinsic factor antibody — Your doctor may order special tests for antibody levels to determine if you have pernicious anemia. Most people who lack intrinsic factor in their stomach have these antibodies in their blood.
Bone marrow biopsy — Occasionally, a bone marrow biopsy is done to help confirm the diagnosis. In this procedure, a small sample of bone marrow is taken by inserting a needle into the pelvic bone just below the waist on either side of the spine. The bone marrow sample is examined in a laboratory to look for other causes of anemia and red blood cell abnormalities.
With proper treatment, symptoms of vitamin B12 deficiency begin to improve within a few days. In vegans and other people whose B12 deficiency is diet-related, oral B12 supplements and a diet designed to increase consumption of vitamin B12 should cure the condition. People with pernicious anemia or people who cannot absorb vitamin B12 from their intestines will need injections of vitamin B12 every one to three months indefinitely.
To prevent vitamin B12 deficiency, vegans should take adequate amounts of vitamin B12 supplements to make up for the shortage in their diet.
For people who cannot absorb B12, the condition cannot be prevented. However, once it is diagnosed, regular injections of vitamin B12 will prevent symptoms from returning.
Treatment for this condition involves replacing the missing vitamin B12. People who cannot absorb B12 need regular injections. When injections first are administered, a patient with severe symptoms may receive five to seven during the first week to restore the body's reserves of this nutrient. A response usually is seen within 48 to 72 hours, with brisk production of new red blood cells. Once B12 reserves reach normal levels, injections of vitamin B12 will be needed every one to three months to prevent symptoms from returning. People who cannot absorb vitamin B12 should continue to eat a well-balanced diet that provides other nutrients (folic acid, iron and vitamin C) necessary to produce healthy blood cells. Sometimes people can take high doses of oral B12 to provide replacement instead of undergoing injections, but a physician should closely supervise this.
In people whose vitamin B12 deficiency is related to overgrowth of intestinal bacteria, treatment with oral antibiotics, such as tetracycline (sold under several brand names), may stop bacterial overgrowth and allow the absorption of vitamin B12 to return to normal.
Vitamin B12 deficiency resulting from inadequate dietary intake is the easiest to treat. The condition can be reversed by taking oral vitamin B12 supplements and adding foods containing B12.
When the anemia is severe and the red blood cell count is extremely low, blood transfusions may be necessary for the first couple of days until the vitamin B12 injections begin working.
When To Call A Professional
Contact your doctor for a physical examination if you experience unexplained fatigue, palpitations, shortness of breath, sore tongue or any other symptoms of vitamin B12 deficiency. This is especially true if you are a vegan, are older than age 50 and of African-American or Northern-European descent, have diabetes, have an autoimmune disorder or have had your stomach removed.
The outlook is excellent because this form of anemia responds well to treatment. However, it is possible that nerve cell damage will be permanent. Some residual damage to the nervous system may remain in people who sought treatment late in the illness.
Learn more about Vitamin B12 Deficiency
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Symptoms and treatments
National Heart, Lung, and Blood Institute (NHLBI)
P.O. Box 30105
Bethesda, MD 20824-0105
Phone: (301) 592-8573
TTY: (240) 629-3255
Fax: (301) 592-8563
Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.